Studies will be continued on the kinetic mechanisms of glutathione peroxidase from rat liver and lung. The selenium prosthetic group will be studied by GLC-mass spectral analysis. The in vivo and in vitro interactions between heavy metals involved in animal toxicities, e.g., cadmium and mercury will be studied. Studies of in vitro protection by GSH peroxidase to enzymes sensitive to lipid peroxidation products will be continued. The response of GSH peroxidase in cells in culture to nutritional levels of selenium will be studied. The new knowledge of the selenium-glutathione peroxidase system will be correlated with the known trace element functions of selenium.